HDFS-11477. Simplify file IO profiling configuration. Contributed by Hanisha Koneru.

hadoop-common-project/hadoop-common/src/site/markdown/Metrics.md

@@ -323,7 +323,12 @@ Each metrics record contains tags such as SessionId and Hostname as additional i
 FsVolume
 --------
 
-Per-volume metrics contain Datanode Volume IO related statistics. Per-volume metrics are off by default. They can be enbabled by setting `dfs.datanode.enable.fileio.profiling` to **true**, but enabling per-volume metrics may have a performance impact. Each metrics record contains tags such as Hostname as additional information along with metrics.
+Per-volume metrics contain Datanode Volume IO related statistics. Per-volume
+metrics are off by default. They can be enabled by setting `dfs.datanode
+.fileio.profiling.sampling.fraction` to a fraction between 0.0 and 1.0.
+Setting this value to 0.0 would mean profiling is not enabled. But enabling
+per-volume metrics may have a performance impact. Each metrics record
+contains tags such as Hostname as additional information along with metrics.
 
 | Name | Description |
 |:---- |:---- |

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -664,10 +664,6 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final int DFS_IMAGE_TRANSFER_CHUNKSIZE_DEFAULT = 64 * 1024;
 
   // Datanode File IO Stats
-  public static final String DFS_DATANODE_ENABLE_FILEIO_PROFILING_KEY =
-      "dfs.datanode.enable.fileio.profiling";
-  public static final boolean DFS_DATANODE_ENABLE_FILEIO_PROFILING_DEFAULT =
-      false;
   public static final String DFS_DATANODE_ENABLE_FILEIO_FAULT_INJECTION_KEY =
       "dfs.datanode.enable.fileio.fault.injection";
   public static final boolean
@@ -676,7 +672,7 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
       DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_KEY =
       "dfs.datanode.fileio.profiling.sampling.fraction";
   public static final double
-      DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_DEAFULT = 1.0;
+      DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_DEFAULT = 0.0;
 
   //Keys with no defaults
   public static final String  DFS_DATANODE_PLUGINS_KEY = "dfs.datanode.plugins";

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/FileIoProvider.java

@@ -62,7 +62,7 @@ import static org.apache.hadoop.hdfs.server.datanode.FileIoProvider.OPERATION.*;
  *
  * Behavior can be injected into these events by enabling the
  * profiling and/or fault injection event hooks through
- * {@link DFSConfigKeys#DFS_DATANODE_ENABLE_FILEIO_PROFILING_KEY} and
+ * {@link DFSConfigKeys#DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_KEY} and
  * {@link DFSConfigKeys#DFS_DATANODE_ENABLE_FILEIO_FAULT_INJECTION_KEY}.
  * These event hooks are disabled by default.
  *

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/datanode/ProfilingFileIoEvents.java

@@ -18,6 +18,7 @@
 
 package org.apache.hadoop.hdfs.server.datanode;
 
+import static java.lang.Math.abs;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.classification.InterfaceAudience;
@@ -43,18 +44,32 @@ class ProfilingFileIoEvents {
 
   public ProfilingFileIoEvents(@Nullable Configuration conf) {
     if (conf != null) {
-      isEnabled = conf.getBoolean(DFSConfigKeys
-          .DFS_DATANODE_ENABLE_FILEIO_PROFILING_KEY, DFSConfigKeys
-          .DFS_DATANODE_ENABLE_FILEIO_PROFILING_DEFAULT);
       double fileIOSamplingFraction = conf.getDouble(DFSConfigKeys
               .DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_KEY,
           DFSConfigKeys
-              .DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_DEAFULT);
+              .DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_DEFAULT);
-      if (fileIOSamplingFraction > 1) {
+      if (abs(fileIOSamplingFraction) < 0.000001) {
+        LOG.info(DFSConfigKeys
+            .DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_KEY + " set to "
+            + fileIOSamplingFraction + ". Disabling file IO profiling");
+        isEnabled = false;
+      } else if (fileIOSamplingFraction < 0.000001) {
         LOG.warn(DFSConfigKeys
             .DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_KEY +
-            " value cannot be more than 1. Setting value to 1");
+            " value cannot be less than 0. Disabling file IO profiling.");
+        isEnabled = false;
+      } else if (fileIOSamplingFraction > 1) {
+        LOG.warn(DFSConfigKeys
+            .DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_KEY +
+            " value cannot be more than 1. Setting value to 1 and enabling " +
+            "file IO profiling");
+        isEnabled = true;
         fileIOSamplingFraction = 1;
+      } else {
+        LOG.info(DFSConfigKeys
+            .DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_KEY + " set to "
+            + fileIOSamplingFraction + ". Enabling file IO profiling");
+        isEnabled = true;
       }
       sampleRangeMax = (int) (fileIOSamplingFraction * Integer.MAX_VALUE);
     } else {

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/datanode/TestDataNodeVolumeMetrics.java

@@ -121,8 +121,8 @@ public class TestDataNodeVolumeMetrics {
 
   private MiniDFSCluster setupClusterForVolumeMetrics() throws IOException {
     Configuration conf = new HdfsConfiguration();
-    conf.setBoolean(DFSConfigKeys
+    conf.setDouble(DFSConfigKeys
-        .DFS_DATANODE_ENABLE_FILEIO_PROFILING_KEY, true);
+        .DFS_DATANODE_FILEIO_PROFILING_SAMPLING_FRACTION_KEY, 1.0);
     SimulatedFSDataset.setFactory(conf);
     return new MiniDFSCluster.Builder(conf)
         .numDataNodes(NUM_DATANODES)

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/tools/TestHdfsConfigFields.java

@@ -107,8 +107,6 @@ public class TestHdfsConfigFields extends TestConfigurationFieldsBase {
         .add(DFSConfigKeys.DFS_DATANODE_STARTUP_KEY);
     configurationPropsToSkipCompare
         .add(DFSConfigKeys.DFS_NAMENODE_STARTUP_KEY);
-    configurationPropsToSkipCompare
-        .add(DFSConfigKeys.DFS_DATANODE_ENABLE_FILEIO_PROFILING_KEY);
     configurationPropsToSkipCompare.add(DFSConfigKeys
         .DFS_DATANODE_ENABLE_FILEIO_FAULT_INJECTION_KEY);
     configurationPropsToSkipCompare.add(DFSConfigKeys